PHYSICAL BASIS OF SENSATION 



6 S7 



primary current the same, and bringing the secondary nearer 

 and nearer the primary, the intensity of the stimulus could 

 be gradually increased quantitatively. The effective intensity 

 of stimulation might also be increased in a graduated 

 manner by fixing the primary inside the secondary, and 

 gradually increasing the duration of stimulation. 



The following record shows the effect of stimuli in- 

 creasing from one to ten, by increments of one at a time 

 (fig. 400). It will be seen that at the beginning, owing to 

 growing sub-tonicity, the nerve was undergoing a gradual 

 relaxation, the downward slope of the beginning of the record. 

 On application of stimulus of intensity as shown by i, there 

 is a sudden responsive 

 relaxation, followed by 

 a partial recovery. As 

 the intensity of stimu- 

 lus is successively in- 

 creased, the positive 

 response undergoes an 

 increase, the maxi- 

 mum-positive response 

 being evoked when the 

 stimulus-intensity is 3. 

 After this the ampli- 

 tude of response undergoes a progressive decline, the response 

 to stimulus 8 being practically zero. This neutral point, as 

 was shown earlier, is not to be regarded as the true zero, being 

 in fact the balancing point of positive and negative. This 

 will be seen when we inspect the record of intensity 9, where 

 the increasing negative actually induces a minute diphasic 

 response positive followed by negative. The next response 

 to stimulus 10 gives us a sudden large negative response. 

 Above this point of transition I find, as will be seen in the 

 following records, that there is a rapid enhancement of normal 

 negative response. Still later, this increase of rate would 

 decline, and later again, by the setting-in of fatigue, the 

 responses might undergo an actual diminution. Thus, in that 



V U 



FIG. 400. Record of Response in Nerve of 

 Gecko showing the Effect of Arithmetically 

 increasing Stimulus 



